1. Field of the Invention
The present invention is in general related to an apparatus that detects scene changes in a source video and selects representative keyframes from each scene. The present invention in particular relates to determining whether a detected scene change is in actuality a scene change or whether a fast motion scene caused a false detection of a scene change.
2. Description of the Prior Art
Users will often record home videos or record television programs, movies, concerts, sports events, etc. on a tape, hard disk or other storage medium for later or repeated viewing. Often, a video will have varied content or be of great length. However, a user may not write down what is recorded on a storage medium and may not remember what she recorded or where on the storage medium particular scenes, movies, events are recorded. Thus, a user may have to sit and view, for example, an entire tape to remember what is on the tape.
Video content analysis uses automatic and semi-automatic methods to extract information that describes content of the recorded material. Video content indexing and analysis extracts structure and meaning from visual cues in the video. Generally, a video clip is taken from a TV program, the Internet or a home video by selecting frames which reflect the different scenes in a video.
In a video indexing scene change detection system described in PHA 23,252, U.S. Ser. No. 08/867,140 a video indexing system is described wherein frames are compared to one another to detect large differences between the frames. If a large difference exists, it is assumed that a scene change has occurred between the two frames. Once the scene change is found, a keyframe is chosen from each scene and the keyframes are arranged to provide a video index. The problem with this system is that during a scene where there is fast motion, such as a car chase scene, the object moving across the scene (e.g. the car) may move from the left hand portion of the frame to the right hand portion of the frame during a plurality of sequential frames. When these frames are compared to each other the prior art system detects a scene change after each frame and selects each frame as a keyframe, when in fact, all frames are from the same scene.
Similarly in PHA 23,477, U.S. Ser. No. 09/123,444 a commercial detection system is disclosed which detects commercials by counting the number of scene changes detected within a time period (xe2x80x9ccut ratexe2x80x9d). Typically commercials have high cut rates and therefore the cut rate can be used to locate and delete commercials from video. If it is determined that the number of scene changes detected during a certain time period is above a certain threshold then it is assumed that a commercial has been detected. The problem with such a system is that a fast motion scene will also have a high cut rate and will be detected as a commercial and possibly deleted from the video.
Accordingly, a system is desired which will create a visual index for a video source that was previously recorded or while being recorded, which is useable and more accurate in selecting significant keyframes, while providing a useable amount of information for a user. This system will detect scene changes and select a key frame from each scene but ignore the detection of scene changes and the selection of key frames where scene changes are detected consecutively after each frame.
It is an object of the invention to compare two frames of a video to detect a scene change, if consecutive scene changes are detected after each frame for a plurality of frames then it is determined that these scene changes are due to fast motion in the video rather than being true scene changes.
It is another object of the invention to count the number of consecutive scene changes to keep track of the length of the sequence of frames having scene cringes detected after each consecutive frame. At the end of this sequence which contains consecutive scene changes, it is determined that all frames within the sequence are part of the same fast motion scene and only one key frame is selected from the sequence.
It is another object of the invention to distinguish fast motion scenes from commercials by analyzing high cut rate video to determine if scene changes occur after each frame.